One of the major challenges in the clinical management of clear cell renal cell carcinoma (ccRCC) is the acquired resistance to targeted therapies. Although microRNAs (miRNA) are potential predictors of cancer progression, to date there are no molecular studies reporting the role of circulating miRNA as biomarkers for predicting response to treatments in ccRCC. Our group has been conducting clinical trials in ccRCC patients with the aim to develop effective combination therapies. We have recently completed a Phase I/II clinical trial to assess the clinical benefit of the histone deacetylase inhibitor (HDACi) vorinostat in combination with the VEGF blocker bevacizumab in patients with prior tyrosine kinase inhibitors (TKIs) and assessed the expression of serum miRNA pre and post treatment. Exiqon microarray analysis has revealed the differential regulation of 134 microRNAs in the post- vs. pre-treatment samples. In particular, in patients who achieved an objective response (Responders) we have observed a significant up regulation of miRNA-605 at baseline as compared to patients who had progressive disease (Progressors). Interestingly, further analysis has revealed that following treatment downregulation of miR-605 expression occurred only in the Responders group. The decrease of miR-605 in the circulation suggests its availability inside the cells. Our bioinformatics prediction algorithms have revealed that SEC24D, a member of coat protein complex II (COPII), is targeted by miR-605. SEC24D is involved in the selection of cargo, concentration, and secretion of biomolecules such as proteins and RNA. To evaluate the effect of HDAC inhibition on SEC24D ccRCC cells were treated with vorinostat and assessed SEC24D expression. We found significant inhibition following HDACi treatment. Furthermore, we observed an increase in intracellular levels and decrease in exosomal miR-605 in 786-0 cells, suggesting an effect of vorinostat on miR-605 secretion. In addition, we also observed the inhibition of mutant p53 expression, as a reported target of miR-605. The current proposed study is aimed to determine a specific miRNA alteration associated with response to epigenetic modulators. Our hypothesis is that the inhibition of SEC24D leads to decrease of extracellular secretion of miR-605 which correlates with response to epigenetic modulators. We have designed the following specific aims to test our hypothesis: Specific Aim 1- To determine the effect of HDAC inhibition on SEC24D and miR-605 in ccRCC cells and patient derived tumor xenografts (PDXs); Specific Aim 2- To assess the correlation between clinical outcome and miR-605 expression in serum from RCC patients receiving HDAC inhibitors in combination with VEGF and PD1/PD-L1 inhibitors. The results from this pilot project will identify a specific circulating miRNA as potential biomarker of response to HDACi treatment that will need to be validated in further prospective clinical studies. Identification of specific molecular alterations of miR-605 and SEC24D in ccRCC patients will provide the rationale for future personalized clinical trials to evaluate the efficacy of HDACi in combination strategies.